Williams sent The Theory of Investment Value for publication before he had won faculty approval for his doctorate. The work discusses Williams' general theory, as well as providing over 20 specific mathematical models; it also contains a second section devoted to case studies. Various publishers refused the work since it contained algebraic symbols, and Harvard University Press published The Theory of Investment Value in 1938, only after Williams had agreed to pay part of the printing cost. The work has been influential since its publication; Mark Rubinstein describes it as an "insufficiently appreciated classic".[4]

Williams was among the first to challenge the "casino" view that economists held of financial markets and asset pricing—where prices are determined largely by expectations and counter-expectations of capital gains[6] (see Keynesian beauty contest). He argued that financial markets are, instead, "markets", properly speaking, and that prices should therefore reflect an asset's intrinsic value.[7] (Theory of Investment Value opens with: "Separate and distinct things not to be confused, as every thoughtful investor knows, are real worth and market price...".) In so doing, he changed the focus from the time series of the market to the underlying components of asset value. Rather than forecasting stock prices directly, Williams emphasized future corporate earnings and dividends.[8]

Developing this idea, Williams proposed that the value of an asset should be calculated using “evaluation by the rule of present worth”. Thus, for a common stock, the intrinsic, long-term worth is the present value of its future net cash flows—in the form of dividend distributions and selling price.[9] Under conditions of certainty,[10] the value of a stock is, therefore, the discounted value of all its future dividends; see Gordon model.

Williams also anticipated the Modigliani-Miller theorem.[16] In presenting the "Law of the Conservation of Investment Value" (Theory, pg. 72), he argued that since the value of an enterprise is the "present worth" of all its future distributions - whether interest or dividends - it "in no [way] depends on what the company’s capitalization is". Modigliani and Miller show that Williams, however, had not actually proved this law, as he had not made it clear how an arbitrage opportunity would arise if his Law were to fail.